It is common practice in certain grinding operations to secure a workpiece located between centers of a grinding machine, lathe or the like, by attaching a driving dog to one end of the workpiece and tightening a set screw which extends through the driving dog and into contact with the workpiece itself. Once the driving dog is secured, a protruding portion thereof is then rotationally driven by means of a drive pin connected to a machine spindle. As a result, the workpiece revolves about a longitudinal axis defined by means of the centers supporting it, thereby allowing grinding operations or the like to be performed.
Loading and unloading a workpiece into and out of a grinding machine utilizing the described type of conventional driving dog system is usually a tedious and time consuming task which tends to adversely offset grinding production rates. A machine operator must manually position the driving dog over each workpiece and then carefully tighten it making sure that alignment is proper and that the set screw is not causing deflection of the sometimes extremely fragile workpieces. After the grinding operation is complete, the driving dog must again be manually and carefully detached from the workpiece and stored separate from the machine in connection with which it is used.
Utilization of a conventional driving dog in order to chuck a workpiece in connection with which precision grinding operations are to be performed thereon presents yet another problem. That is, the necessarily non-symmetrical configuration of a common driving dog, upon rotation, tends to create radial positioning forces which generally push or pull the workpiece off the centers upon which it is mounted. The effect of these forces upon the rotation of the workpiece makes grinding within close tolerances very difficult, if not impossible.
In addition, the non-uniform method by which the driving dog clamps down upon a workpiece will sometimes cause a workpiece to temporarily slip within the driving dog when the workpiece is first rotated, causing the surface of the workpiece to become scratched or marked.